A fluid ejection system typically includes a fluid path from a fluid supply to a nozzle assembly that includes nozzles from which fluid drops are ejected. Fluid drop ejection can be controlled by pressurizing fluid in the fluid path with an actuator, such as a piezoelectric actuator. The fluid to be ejected can be, for example, an ink, electroluminescent materials, biological compounds, or materials for formation of electrical circuits.
A printhead module is an example of a fluid ejection system. A printhead module typically has a line or an array of nozzles with a corresponding array of ink paths and associated actuators, and drop ejection from each nozzle can be independently controlled by one or more controllers. The printhead module can include a body that is etched to define a pumping chamber. One side of the pumping chamber is a membrane that is sufficiently thin to flex and expand or contract the pumping chamber when driven by the piezoelectric actuator. The piezoelectric actuator is supported on the membrane over the pumping chamber. The piezoelectric actuator includes a layer of piezoelectric material that changes geometry (or actuates) in response to a voltage applied across the piezoelectric layer by a pair of opposing electrodes. The actuation of the piezoelectric layer causes the membrane to flex, and flexing of the membrane thereby pressurizes the fluid in the pumping chamber and eventually ejects a droplet out of the nozzle.